1. Field of the Invention
The present invention relates to an apparatus and a method used in a wireless communication system, and more particularly, to an apparatus and a method of handling a multimedia broadcast multicast service (MBMS) service in a wireless communication system.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3GPP Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3rd Generation Partnership Project (3GPP) as a successor of a universal mobile telecommunications system (UMTS), for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple UEs, and communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint transmission/reception (CoMP), uplink (UL) multiple-input multiple-output (MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
Multimedia broadcast multicast service (MBMS) service or evolved MBMS (E-MBMS) service have been introduced in the UMTS, the LTE system and the LTE-A system, for broadcasting multimedia contents such as TV programs, films, music, etc. Comparing with the traditional unicast, the MBMS service (hereafter referred to both the MBMS service and/or the E-MBMS service) is downlink only, and is broadcasted from the network to multiple (e.g., a specific group of) UEs via a point-to-multipoint transmission. Characteristic of the MBMS service enables the network to provide the MBMS service to unlimited number of UEs with a constant network load. Besides, a UE in the UMTS, the LTE system and/or the LTE-A system can receive the MBMS service inherently, and no additional hardware component is needed to be installed for the MBMS service. Thus, the MBMS service is attractive considering both hardware cost and resource efficiency.
However, when the UE is receiving the MBMS service, a display device (e.g., screen) of the UE may be turned off, e.g., by a user of the UE or due to that the UE transfers to a power-saving mode. In this situation, battery life of the UE is wasted, since the user is not watching the multimedia contents broadcasted via the MBMS service while the UE continues receiving the MBMS service. Thus, saving the battery life for the UE receiving the MBMS service becomes a problem to be discussed and solved.